Authentication and authorization of a mobile digital processing device to a network can be based on the identity of the mobile digital processing device or the identity of a card within the mobile digital processing device. For example, IP Multimedia Subsystem (IMS) and Multimedia Domain (MMD) registration and authentication mechanisms are based on pre-configured shared keys in the IMS Subscriber Identity Module (ISIM) and the Home Subscriber Server (HSS). However, these keys and other identifying information are stored in the mobile device. When a user connects to the network, information from the Subscriber Identity Module (SIM), from the mobile device itself (e.g., serial number), or other identifying information is used to authenticate and authorize the mobile device and the account attached to the mobile device. Therefore, if a first person were to share a mobile device with a second person, this second person would be using the first person's account and services because it is the first person's mobile device and the account is attached to that mobile device and/or SIM card. The mobile device can include, for example, a portable phone, a cell-phone, a personal digital assistant (PDA), and/or a laptop computer connected to, for example, a cellular network. Such devices can be referred to as, for example, user equipment (UE) or mobile stations (MS).